FIG. 1 illustrates an arrangement of cylinders, pistons, and crankshafts in an opposed-piston engine. The figure shows a three-cylinder arrangement, although this is not intended to be limiting; in fact, the basic architecture portrayed in FIG. 1 is applicable to opposed-piston engines with fewer, or more, cylinders. The opposed-piston engine 10 includes cylinders 12, each including exhaust and intake ports 14 and 16. Preferably, the cylinders comprise liners (also called “sleeves”) that are fixedly mounted in tunnels formed in an engine frame or block 18. A pair of pistons (unseen in this figure) is disposed for opposing reciprocal movement in the bore of each cylinder 12. The opposed-piston engine 10 includes an interlinked crankshaft system including two rotatably-mounted crankshafts 21 and 22 and a crankshaft gear train 30 linking the crankshafts and coupling them to a power take-off shaft (“PTO shaft”). The crankshafts 21 and 22 are mounted to the engine by main bearing arrangements (not shown), one at the bottom of the engine block 18 and the other at the top. The crankshaft gear train 30 is supported in one end of the engine block 18 and is contained in a compartment 31 therein that is accessed through a removable cover 32.
As per FIG. 1, one piston of each piston pair is coupled to a respective crank journal 23 of the crankshaft 21 by a connecting rod assembly 27; the other piston is coupled to a respective crank journal 25 of the crankshaft 22 by a connecting rod assembly 29. The crankshafts 21 and 22 are disposed with their longitudinal axes in a spaced-apart, parallel arrangement. The crankshaft gear train 30 includes a plurality of gears, including two input gears 36a and 36b, which are fixed to respective ends of the crankshafts 21 and 22 for rotation therewith. An output gear is mounted for rotation on a fixed shaft or post. The output gear 37 drives a power take-off shaft 38 about an output axis of rotation A. In this configuration, two idler gears 39a and 39b are provided, each mounted for rotation on a fixed shaft or post. The idler gear 39a meshes with the input gear 36a and the output gear 37; the idler gear 39b meshes with the input gear 36b and the output gear 37. As a result of the configuration of the crankshaft gear train 30, the crankshafts 21 and 22 are co-rotating, that is to say, they rotate in the same direction. However, this is not meant to so limit the scope of this disclosure. In fact, a gear train construction according to this specification may have fewer, or more, gears, and may have counter-rotating crankshafts. Thus, although five gears are shown for the crankshaft gear train 30, the numbers and types of gears for any particular crankshaft gear train are dictated only by the engine design. For example, the crankshaft gear train 30 may comprise one idler gear for counter-rotation, or two idler gears (as shown) for co-rotation.
The gear train 30 shown in FIG. 1 represents a desirably convenient way to connect two crankshafts of an opposed-piston engine for stable operation and to unify the outputs of the crankshafts for delivery to a drive train via the power take-off shaft. In addition to a crankshaft gear train, a multispeed transmission is needed to convert the engine's output (speed and torque) as necessary to meet operating conditions of a drive train. In this regard, the term “transmission” also refers to a drive mechanism or gearbox comprising transmission gears arranged to selectably obtain speed ratios that match engine output to drive train requirements. In many instances, a gearbox matches engine output to the wheel speeds of a vehicle or a locomotive, or to propeller speeds of an aircraft or vessel. If the crankshaft gear train and the gearbox are provided as separate units, with torque input to the gearbox via the power take-off shaft, considerable redundancy is encountered in packaging, and the length of the drive train is necessarily extended. Combining the crankshaft gear train and the gearbox into a single unit in which an arrangement of gears receives torque inputs directly from the spaced-apart crankshafts would offer potential benefits in reducing the weight and size of the engine, and the length of the drive train.
U.S. Pat. No. 3,340,748 describes a multi-engine drive mechanism which couples two engines of an aircraft to drive a single propeller shaft by way of a single drive mechanism. The drive mechanism receives a torque input from one engine, or respective torque inputs from both engines, and allows the propeller shaft to be driven by either or both of the engines. The drive mechanism automatically establishes a predetermined speed ratio between the engines and the propeller shaft when both engines operate at the same speed. When one engine ceases operation, the drive mechanism automatically changes the speed ratio between the still operative engine and the propeller shaft in order to optimally drive the aircraft. Of course, the matter of driving a single output shaft from two independent engines involves complex mechanical logic that must be able to combine torque inputs from independent sources and dynamically adapt to different torque input combinations. In any case, the speed ratios remain fixed. In the case of a single opposed-piston engine with two crankshafts, however, the challenge is to combine two continuously-operating torque inputs in a single drive mechanism equipped to obtain various speed ratios.